Instant soluble coffee products, such as freeze-dried and spray-dried instant coffee, are well known. An example of a freeze-dried instant coffee is Kenco® Smooth freeze dried coffee. Such instant soluble coffee products are formed by deriving a liquid coffee concentrate intermediate (commonly known as coffee liquor) from coffee beans by the well known processes of roasting and extraction. Optionally, the coffee concentrate may be aromatized by the addition of coffee aromas stripped from an extracted coffee intermediate, again as well known in the art. The coffee concentrate is then subjected to various foaming and drying steps to produce a dry granular end product that can be reconstituted into a coffee beverage by the addition of hot water.
Instant soluble coffee products are popular with consumers as they provide an economical, fast and simple way of preparing a coffee beverage. However, there has been a desire to produce instant soluble coffee products which are more reminiscent of roasted ground coffee products both in the appearance of the product prior to reconstitution and when consumed.
It is known to incorporate in a soluble coffee product a percentage of roasted ground coffee in order to attempt to produce a more appealing instant soluble coffee product. For example, WO2010/005604 describes various soluble coffee products blended from soluble and ground coffee components.
A problem that the present applicant has found with soluble coffee products incorporating a roasted ground coffee component is that it is difficult to adequately disperse the roasted ground coffee particles within the liquid coffee concentrate intermediate. Poor dispersion can lead to clumping of the roasted ground coffee particles on addition to the liquid coffee intermediate leading to non-hydrated regions of roasted ground coffee which never fully ‘wet’.
Partly in order to try and overcome the problem of poor dispersion it has been known to try and reduce the roast and coffee particle size down to colloidal particle sizes of less than about 30 to 40 microns. For example, U.S. Pat. No. 4,594,257 describes an agglomerated instant coffee product comprising spray-dried instant coffee and roasted coffee colloidal particles having a particle size of 5 to 25 microns.
However, in order to produce colloidal sized particles of roasted ground coffee it is necessary to utilise special grinding processes since the coffee oil contained in the roasted ground coffee has a tendency to be released when the particles are ground to such a small size. Coffee oil release leads to detrimental affects on the grinding process such as clumping of the coffee particles and fouling of the grinding machine surfaces necessitating regular machine cleaning and consequent down time.
In order to overcome this problem it is known to cryogenically pre-freeze the roasted coffee beans prior to them being ground down to colloidal sizes. For example, in WO2010/005604 the roasted coffee beans are frozen to a temperature of about −5° C. and then pulverised into particles with a mean or median particle size of about 350 microns or less. In another example, GB2022394 describes a process of quenching roasted coffee beans in liquid nitrogen before being ground to a particle size of less than 45 microns.
The requirement to cryogenically freeze the roasted coffee beans prior to grinding increases the complexity and expense of the manufacturing process.
Another suggested solution to permit colloidal grinding of roasted coffee beans is to add additional oil to the grinding mixture to provide additional lubrication. Whilst this can in some situations overcome the problem of fouling of the grinding machine surfaces it results in a ground coffee product with a high oil content that is not ideal for use as a coffee intermediate for further processing into an instant soluble coffee beverage since only a relatively small amount can be added to products without a detrimental affect on the product composition.
Another suggested solution in EP1631151 is to add an additional component such as cocoa mass or sugar to absorb any coffee oil released by the roasted and ground coffee. However, this process is unsuitable where the desire is to use the colloidal roasted ground coffee in a pure soluble coffee beverage.
Another known desire is to attempt to make the visual appearance of the instant soluble coffee product more like that of roasted ground coffee. Typically, instant soluble coffee products are lighter in colour than roasted ground coffee. There has therefore been a desire to darken the colour of instant soluble coffee products, in particular freeze-dried soluble coffee. Prior art methods for darkening the colour of soluble coffee include the use of steam darkeners as described in EP0700640 and re-wetting of a freeze-dried intermediate as described in EP0090561. In addition CO2 gasification has been used to darken soluble coffee products.
However, prior art techniques for darkening the appearance of a soluble coffee product have certain drawbacks. Re-wetting of the intermediate coffee product by addition of water or use of steam or the use of gases, such as CO2, can alter the density and solubility of the end product.